PS中的 另存为 与 另存为网页格式下

ICC Color Profiles

Both Save for Web and Save As give you the option of including the ICC Color Profile within the image. Color profiles are used to the viewer's display how the RGB values within the image data should map to real-world colors. Assuming you have a color-managed environment (calibrated and profiled monitor), this profile is used to display the colors as they were intended to be shown.
Unfortunately, most web browsers don't read this profile and most people don't have calibrated monitors, so the default color space, sRGB is generally assumed. Therefore, if you are sharing your photos on the web, and your photos were shot in a color space such as Adobe RGB, it is strongly advised that you convert to sRGB first. Once you've done that, there is little need to include the ICC profile within the file.
Comparison of JPEG Markers
The differences between the output of the two JPEG compressed file saving methods is easily visible when comparing the JPEG (JFIF) files themselves. The JPEG (JFIF) file format specifies a number of mandatory markers as well as some optional ones. The chart below shows how Photoshop CS2 Save as and Photoshop CS2 Save for the Web compare at a low level, with the help of JPEGsnoop:

ICC颜色配置：

另存为网页格式和另存为都提供了是否嵌入ICC颜色配置的选项。颜色配置是用来让图片文件的RGB数值在用户显示器上显示出更真实的色彩。假设你有一个经过颜色管理的环境（校准和配置过的显示器）配置能让颜色显示更接近预期的效果。
很不幸的是，大部分浏览器不支持颜色配置，并且大部分人没有校准过的显示器，所以默认假设是sRGB色彩空间。因此，如果你在网上分享照片，如果你的照片拍摄时使用的是其它色彩空间，例如Adobe RGB，那么强烈建议你转换为sRGB。如果你这样做的话，就基本不需要在文件中嵌入ICC颜色配置了。
通过对比jpeg文件，两种jpeg压缩文件保存方式的区别是很容易识别的。jpeg（jfif）文件格式中列入了一些强制的标记和一些可选的标记。

下面的表格是photoshop另存为和另存为网页格式的输出文件的对比

Comparison of JPEG Markers in Photoshop

As can be seen in the above table, the additional data stored within a Save As JPEG versus as Save for Web JPEG is typically in the order of ~ 40 KB. In most high-resolution photos, this extra is insignificant, but when trying to compress small images for web use, this overhead could be significant

Photoshop两种保存方式输出文件的jpeg标记对比

如上表所示，另存为输出文件所包含的附加信息使文件比另存为网页格式多40kb。对于大部分高分辨率的图像文件来说，这部分数据并不明显，但如果想要压缩图像文件大小以供网页使用，那么这部分就很明显了

Extraction of Quality Setting in Save As

In files generated using Save As, you can derive the quality setting from the Photoshop IRB resource (0x0406) in the JPEG APP13 (0xFFED) marker. The following hex view is of an image saved with quality setting 2.
（图见下）

Value  Quality
0xFFFD Quality 1 (Low)
0xFFFE  Quality 2
0xFFFF Quality 3
0x0000  Quality 4
0x0001 Quality 5 (Medium)
0x0002  Quality 6
0x0003  Quality 7
0x0004  Quality 8 (High)
0x0005 Quality 9
0x0006  Quality 10 (Maximum)
0x0007 Quality 11
0x0008 Quality 12 

另存为的图像质量设置

在用另存为方式输出的文件中，你能根据JPEG APP13 (0xFFED)标记中的photoshop IRB资源(0x0406)数据推得图片质量的设置值。下面是一副保存质量为2的图片文件的16进制视图。

数值 质量
0xFFFD 质量1 (低)
0xFFFE  质量2
0xFFFF 质量3
0x0000  质量4
0x0001 质量5 (中)
0x0002  质量6
0x0003  质量7
0x0004  质量8 (高)
0x0005 质量9
0x0006  质量10 (最佳)
0x0007 质量11
0x0008  质量12

Extraction of Quality Setting in Save For Web

In files generated using Save For Web, you can derive the quality setting (1..100) from the Ducky resource in the JPEG APP12 (0xFFEC) marker (starts with null-terminated ASCII string Ducky). The percent value is stored in hex. The following hex view shows a file saved with quality setting 51 = 0x31:（图见下）

另存为网页格式的质量设置

在另存为网页格式的图片文件中，你能根据JPEG APP12 (0xFFEC)标记(以空数据开头、ASCII编码Ducky结束)中的Ducky资源推得图像质量设置（1－100％）数据是以16进制保存的。图中在0x31处，16进制数值33表示图片质量为51。

Comparison of Save As vs Save For Web Quality

Many people are confused about why there is a difference in the definition of quality settings within Photoshop and furthermore, how they compare. The following table shows the two methods and the relative ordering of quality between the settings, from best to worst quality. See description below for the limitations of such an ordered comparison.
For more information: read about JPEG chroma subsampling.

Method JPEG Quality Preset Chroma Subsampling
Save For Web 100 Maximum 1x1
Save As 12 Maximum 1x1
Save For Web　 90     1x1
Save As　 11     1x1
Save For Web　 80 Very High 1x1
Save As 10     1x1
Save For Web 70     1x1
Save As 9     1x1
Save For Web 60 High 1x1
Save As 8 High 1x1
Save For Web 51     1x1
Save For Web 50     2x2
Save As 6     2x2
Save As 7     1x1
Save As 5 Medium 2x2
Save For Web 40     2x2
Save As 4     2x2
Save As 3 Low 2x2
Save For Web 30 Medium 2x2
Save As 2     2x2
Save For Web 20     2x2
Save As 1     2x2
Save For Web 10 Low 2x2

In graphical form, here is a chart that shows a comparison of the JPEG luminance and chrominance across the default presets, each with the equivalent JPEG standard "quality factor". Of course, it is important to note that the quality factor shown is not an accurate measure of image quality since they are only truly comparable quantities if both Save for Web and Save As were based on linear scalings of the quantization tables included in the JPEG Standard Annex. Since neither is based on the sample tables, the quality factor should only be taken as a very rough comparison measure. The graph is ordered by decreasing luminance quality factors.
（图见下）
Ordered Graph
（图见下）
Comparison Graph

另存为和另存为网页格式的比较

很多人对为何photoshop中的两种保存方式质量设定的定义有区别而不解，还有怎么比较他们。下面的表格是两种保存方法设置质量后的图像质量排序，从最佳质量到最低质量。这种排序比较的局限性请看后面的说明。
更多信息请查阅jpeg色度抽样。

Method JPEG Quality Preset Chroma Subsampling
另存为网页格式 100 最佳 1x1
另存为 12 最佳 1x1
另存为网页格式　 90     1x1
另存为 11     1x1
另存为网页格式 80 较高 1x1
另存为 10     1x1
另存为网页格式 70     1x1
另存为 9     1x1
另存为网页格式 60 高 1x1
另存为 8 高 1x1
另存为网页格式 51     1x1
另存为网页格式 50     2x2
另存为 6     2x2
另存为 7     1x1
另存为 5 中 2x2
另存为网页格式 40    2x2
另存为 4    2x2
另存为 3 低 2x2
另存为网页格式 30 中 2x2
另存为 2     2x2
另存为网页格式 20     2x2
另存为 1     2x2
另存为网页格式 10 低 2x2

下面是默认设置下的jpeg亮度和色度的对比图表，每个都有对应的jpeg标准质量系数。当然，有必要指出，质量系数不是测量图片质量的精确标准，只是如果另存为网页格式和另存为都是基于jpeg标准附录中的量化表的线性测量，那么质量系数是唯一能用来比较图片质量的参数。质量系数只能作为一个粗糙的标准来比较图片。图表按亮度质量系数降序排列

排序图表

对比图表